Typically in the preparation of tissue specimens for microscopic examination, the specimens are subjected progressively to fixation, dehydration, clearing and embedding in a suitable wax to facilitate sectioning of the tissue specimens. The sectioned specimens may then be further treated to permit their staining and mounting for examination. The dehydration stage usually involves the treatment of a batch of specimens with alcohol reagents of progressively increasing concentration, and the clearing stage involves the treatment of these dehydrated specimens one or more times with a clearing agent such as xylene to displace the alcohol. An analogous preparation technique now coming into favour substitutes a resin impregnation/embedding stage for the wax-embedding procedure that conventionally follows the described dehydration and clearing stages. The resin impregnation/embedding stage may, for instance, consist in first impregnating the dehydrated specimens with a resin solution containing an inhibited activator, followed by infiltrating the impregnated specimens with a hardener solution that enables the activator to accomplish curing of the resin. The treatment of sectioned specimens for staining typically involves dewaxing or etching and rehydration in one or more stages, and the staining procedure (using aqueous stains or immunostaining techniques) is usually followed by a treatment with an agent compatible with the mountant used for coverslipping the section.
Apparatus used for these treatments falls into two general classes: single-container appratus as discussed below; and multi-container apparatus in which there is a plurality of containers that in use respectively contain the various individual reagents, a specimen or a batch of specimens, typically contained, perhaps in cassettes, in an openwork basket, being transported to each (or a selection) of the containers in a prescribed sequence to be immersed in the respective reagents therein to accomplish the required treatment steps. Typically the reagent-containing containers are disposed in a circle and a specimen basket is supported on a radial arm so as to be capable of being raised and lowered into and out of a selected container, relative rotation between the arm and the circle of containers serving to position the basket for introduction into a particular container. Modern apparatus of this type is significantly automated and capable of carrying out a treatment sequence involving immersion of tissue specimens, in the basket, for selected individual periods of time in a preselected sequence of the reagent-containing containers.
In general, apparatus of this multi-container type is so arranged that there is considerable exposure of the tissue specimens to the ambient atmosphere in the intervals between successive immersions of the specimens in the respective reagents. Because the reagents are, typically, volatile there is substantial loss of reagent vapour to the local atmosphere as well as the risk of reagent splashing and contamination of the environment of the apparatus. Moreover, sometimes the tissue specimens to be treated are noxious or toxic so that their unrestrained exposure to ambient atmosphere gives rise to unacceptable local contamination, necessitating operation of the apparatus within an appropriate enclosure.
Both to mitigate this problem of environmental contamination and to provide other advantages, there has recently been developed the single-container apparatus in which there is a single processing container for the reception of one or more tissue specimens and to which reagents are supplied, in turn, for the sequential treatment of the tissue specimen(s) therein with such reagents. An example of an apparatus of this kind is disclosed, for instance, in U.S. Pat. No. 4,604,964 (Gordon et al) that provides for substantially total containment within the apparatus, during the operation thereof, of the specimen(s) being treated, all the reagent liquids and any vapours thereof. Such single-container apparatus is, however, typically of considerably greater capital cost than multi-chamber apparatus and an objective of the present invention is to provide a multi-container apparatus that is so constructed and arranged as to achieve substantial containment of specimens, reagent liquids and their vapours within the confines of the apparatus during operation thereof, thereby to obtain the containment advantages of the single-container apparatus without the concomitant cost and complexity.